1. Field of Invention
The present invention relates to a one-step method for loading a drug coating onto an interventional device. Particularly, the present invention is directed to a method of mixing a drug with a phosphorylcholine-linked methacrylate polymer in a liquid and applying the mixture to an interventional device, such as a stent, in a single step.
2. Description of Related Art
Cardiovascular disease is prevalent in the United States and in other parts of the world. One manifestation of cardiovascular disease is atherosclerosis, which is the buildup of plaque (or fatty deposits) on the walls of blood vessels, such as coronary arteries. This buildup of plaque can grow large enough to reduce blood flow through the blood vessel. Serious damage results when an area of plaque ruptures and forms a clot, which travels to another part of the body. If the blood vessels that feed the heart are blocked, a heart attack results. If the blood vessels to the brain are blocked, a stroke results. Thus, atherosclerosis can be fatal for some people.
Percutaneous transluminal coronary angioplasty (PTCA) is a procedure for treating atherosclerosis. Angioplasty is the mechanical widening of an obstructed blood vessel. This procedure generally entails introducing a catheter assembly into the cardiovascular system of a patient via the brachial or femoral artery. Once introduced, the catheter assembly is advanced through the coronary vasculature until the balloon portion of the catheter assembly is positioned across an occlusive lesion. When positioned across the lesion, the balloon is inflated to a size sufficient to radially compress the plaque against the vessel wall. Subsequently, the balloon is deflated to allow the catheter assembly to be withdrawn from the vasculature of the patient.
While PTCA is widely used, it suffers from two unique problems. First, the blood vessel may suffer acute occlusion immediately after or within the initial hours after the dilation procedure. Such occlusion is referred to as “abrupt closure.” Abrupt closure occurs in approximately five percent of cases in which PTCA is employed. The primary mechanisms of abrupt closures are believed to be elastic recoil, arterial dissection and/or thrombosis. The second problem associated with this procedure is the re-narrowing of an artery after an initially successful angioplasty. This re-narrowing is referred to as “restenosis,” which among other things, typically occurs within the first six months after angioplasty. Restenosis is believed to be due to the proliferation and migration of cellular components from the arterial wall, as well as through geometric changes in the arterial wall referred to as “remodeling.”
To overcome some of the drawbacks of angioplasy, such as reducing occlusion of the artery, thrombosis formation and/or restenosis, it is known to implant an expandable interventional device or prosthesis to maintain patency. One example is a stent. A stent is a mesh tubular member used to prop open a lumen. The stent is collapsed onto a catheter or stent delivery device and travels to the area of blockage while secured onto the catheter. The stent is positioned across the blockage or lesion and radially expands to prop open the blood vessel.
To better effectuate the treatment of atherosclerosis and other cardiovascular diseases, it is beneficial to load an intraluminal device or prosthesis with one or more therapeutic agents, such as antiproliferatives, for delivery to a lumen. One commonly applied technique for the local delivery of a drug to a stent, for example, is through the use of a polymeric carrier coated onto the surface of a stent, as disclosed in Berg et al., U.S. Pat. No. 5,464,650, the disclosure of which is incorporated herein by reference. Berg's method of loading drug onto the stent, however, requires multiple repetitive coating steps to achieve uniformity and control over the amount of therapeutic substance to be applied to the stent. Furthermore, Berg requires an evaporation step so that the coating of the final product includes the drug and polymer but little or no residual solvent.
Although conventional methods and products such as those taught by Berg generally have been considered satisfactory for their intended purpose. Such conventional methods are inefficient and costly due to the requirement of separate, multiple coating and time for sufficient evaporation. Additionally, each additional step of such conventional processes require additional manipulation of the stent being coated. Because stents are, by their very nature, fragile devices, additional manipulation increases the risk of physical damage and contamination of the stent. There thus remains a need for an efficient and economic method and system for loading a drug into a polymer coating for application to a stent with a minimum amount of manipulation of the stent or similar device and to allow for uniform distribution of the polymer coating.